Induced draft heater



March 8, 1949.

J. F. FISHER INDUCED DRAFT HEATER 2 Shets-Sheet 1 Filed Jan. 29, 1947 March 8, 1949. J. F. FISHER 6 I INDUCED DRAFT HEATER Filed Jan. 29, 1947 2 Sheets-Sheet 2 In ueni l'.

Patented Mar. 8, 1949 UNITED STATES PATENT OFFICE INDUCED DRAFT HEATER Application January 29, 1947, Serial No. 725,001

8 Claims. 1

This invention relates to a heater or furnace especially adapted for use in mechanically operated heating systems providing heat and hot water supply for buildings, and in industrial operations in which relatively small quantities of heat or steam are required. More particularly, the invention is concerned with a new form of heater of the induced draft type in which a portion of the flue gases is returned to the heat exchange zone to produce therein a novel effect and provide a more efficient heat exchange between 'the boiler and the products of combustion resulting from the burning of a carbonaceous fuel. The mechanically operated apparatus of the invention, which is adaptable to hot air, hot water or steam heating systems, may be automatically controlled and may be fired with liquid, gaseous, or solid fuel. When solid fuel is employed, the new heater affords particular advantages over other types of heaters now available by providing a dustless heating system. The invention further includes within its scope a new form of boiler or heat exchange apparatus for use in a heating system which produces an eflicient heat transfer between hot gases supplied to it from any source and a heat conveying medium,

In the heating systems of the domestic class heretofore proposed or employed, the attainment of high heat exchange efliciency has been a major problem, and in spite of signal advances, heat recovery expressed in terms of potential heating power of the fuel has not achieved a high level. Many different arrangements of firebox and combustion zone in combination with complex boiler or hot air circulating systems have been designed to produce a maximum area of heat exchange surface. In producing such increased surfaces, in a necessarily confined space, however, the path of travel of the heated gases becomes tortuous with an attendant decrease in velocity, which is undesirable, since heat transfer is proportional to the velocity of hot gases across the heating surfaces. An increase in permissible pressure at the burner to increase velocity of flow of combustion products is limited because of the danger of building up too great a back pressure in the firebox and causing products of combustion to escape to the atmosphere, a condition which cannot be tolerated in domestic units. Furthermore, such an increase in pressure would involve an unwarranted complexity in the burner and air supply equipment. In heating systems involving coal stokers, difficulties are often encountered due to soot and fly ash formation.

and deposition on the internal heat exchange 2 surfaces with resulting loss in heat transfer efficiency.

The present invention is accordingly directed to the provision of a heater or furnace which is simple in construction and operation, which involves a principle of operation different from those previously employed, and which eliminates or minimizes the disadvantages of the prior types. In the new heater of my invention, combustion supporting air is drawn into the firebox adjacent the burner by an induced draft produced by a fan situated beyond the heat exchange zone and outside the body of the furnace. A controlled portion of the gases withdrawn by the fan is returned to the hot gases within the heat exchange zone to increase their velocity. The control of the volume of recirculated gas also serves to control the intake of combustion air at the burner.

The preferred form of the new heater includes a drum forming the principal reservoir for the heat conducting medium, and inner and outer spaced walls extend downwardly from the drum and are connected at their lower ends to form an outer annular leg in communication at its top with the interior of the drum. Another pair of inner and outer walls lead downwardly from the drum within the outer leg and are connected at their lower ends to form an inner annular leg in communication at its top with the interior of the drum. The inner leg defines a combustion chamber open at the bottom, and the hot gases of combustion from fuel burned in a firebox below the lower ends of the legs, flow upwardly through the combustion chamber and are defiected outwardly by the bottom of the drum to flow through openings in the inner leg into the annular gas space between the legs. A gas outlet passage and a gas inlet passage extend through the outer leg near the bottom and top thereof, respectively, and the inlet passage and, preferably, also the outlet passage, are tangential to the inner surface of the outer leg and at an angle to one another. The heater includes means, such as a fan, for withdrawing gases through the outlet passage, and a controlled portion of the gases is returned through the inlet passage. The gases so returned mix with the deflected hot gases and flow therewith spirally downwardly along the inner surface of the outer leg to the outlet passage.

A simpler form of the new heater is of the construction above described, except that the inner leg is omitted and the combustion chamber is defined by the outer leg. In this construction,

as in the preferred form, the hot gases flowing upwardly through the combustion chamber are deflected outwardly by the bottom of the drum toward the inner wall of the leg and mix with return gases entering the chamber through the tangentially disposed inlet passage. The mixture of gases then flows spirally downwardly along the inner surface of the leg to the outlet passage.

In order that my invention may be clearly understood, it will be described with reference to the accompanying drawings showing a pre-. ferred form of apparatus in accordance with the invention in which heat is supplied by an under-. fed rotating coal stoker similar to that disclosed in the G. M. Peltz, U. S. Patent No. 2,127,933.

Fig. 1 is a vertical sectional view showing the complete assembly of parts;

Fig. 2 is a top plan view of the apparatus of Fi l;-

Fig. 3 is a sectional view on the line 33- 3 of F g- Fig. 4 is a sectional view on the line 4-4 of Fi d.

Fig. 5 is a fragmentary section through the firebox showing the ash removal system.

In the. form of apparatus illustrated, a vertically disposed firebox 5, having an opening 6 closable by a transparent plate l, rests upon an open base 8. An underfed burner or retort 9 surrounded by skirt member l0; is situated in the firebox and passes through the floor H to connect with a fuel supply pipe 12, through which the coal is conveyed by a screw or worm conveyor it from a bin or hopper (not shown). A short extension screw M mounted on a common drive shaft and having flights pitched in the opposit direction from those on the conveyor, cooperates to force the coal upwardly through the retort. Drive shaft I5 is actuated by intermediate driving means it which is connected to electric motor ll which also provides power for the other moving parts of the equipment. The operation of this motormay be controlled by thermostatic means responsive to. the air temperature in a room or to the water temperature in the system in accordance with well known principles.

The boiler portion of the heater includes, a cylindrical casing #8: supported on the top of the firebox 5 and closed at the top by circular plate la9i having outlet connection 2%. An annular partition 2t lies concentric with'and spaced inwardly from casing l8 and is connected thereto at its lower end by a closure 22. A horizontal plate 23 closes the top of the combustion chamber and serves as a floor for a drum or reservoir for the heat conveying medium, ordinarily water. The interior of the drum is in communication with the space 25, between the casing and partition 255;, and the space thus serves as a water leg.

Spaced concentric partitions 2B and '27 extend downwardly within partition 2! from the floor of the drum and are. connected at their lower ends by an inwardly and upwardly sloping wall to form an inner annularwater leg 29. The partitions are closed at thei-r'upper ends byan upwardly and outwardly sloping wall 36. and the water leg 2'9 is connected to reservoir 24 by a plurality of spaced pipes 3:1 leading from openings 3 2 in wall tfito openings :33 in floor23. Thewater legs 25 and 29 are in communication in their lowerportions throughdiametrically located connections 3 and 34', thus permitting good circulation of water through the two circular legs and th reservoir. Return water from the outside system enters the boiler through connections 35 and 35' leading to the outer water leg near the lower end thereof, and the heated water or steam leaves th boiler through outlet connection 20. Annular partition 21 defines a central vertical cylindrical cembustion zone 3'6 open at its bottom to form an extension of the firebox 5 and situated directly over the burner 9. The combustion zone is connected with annular gas space 3? between'the water legs via openings 38 located between the water pipes 3|.

Qutside. of the boiler proper, a duct 39, which serve as a housing for fan 4!] actuated by motor I7, is connected through restricted opening 4|, breeching' 52, andopening 43 in the outer water leg 25. to the annular gas space 3?. As shown in Figs. 2 and 4, the outlet passage through opening 4.3. is Subs ant a y ang nt t the ann ar as space 3' Conduit 3.9 is. connected thr box 8J4 attached to outer wall l8, to a flue 45. At the bottom of space l' l'is sloping ba'file 46,"w'hi.,ch causes a han e n irection of t e ases mpelled up.- W-ardly by fan 60, and the baffle, together with th sloping surface 41 at the bottom of box l' l, directs, them toward opening' la, the size of which is controlled by reciifiulation damper 059. This arrangement permits the return of a predetermined desired proportion of the products OI combustion to. the annular gas. space 3-1 nearthe top thereof through a passage through the-outer w ter g 25.. Passa 5B is substa t a y ta gent to the gas space 3.1, as, shown in Figs. 2. 13,

and complementary to, and above the tangential outlet passage 4.3,.

Various other arrangements. are possible in this part of the structure to; control the proportion of gases from theta-n discharge. which are returned to. the heat exchange zone near the top thereof. A flap. damper, for example, may replace sliding damper 49 and this-change may render the baffle 16. unnecessary.

n the, hea r tra ed, t e. tort o state 9 is made up of a series of rings of increasing diameter mounted one. upon the other and constructed to provide slotted air passages for ad mission of air uniformly to the bed of fuelin the retort. The retort, is supported on a bearing 5| for rotation on a vertical axis. by any suitable means, and may be driven through, bevel gearing (not shown) by avertical shaft 52 connected through bevel gearing 53. and; a coupling 54. to an extension of a shaft, driven from motor H through a pulley -56. Ashes are discharged over the top edge of the retort and fall; upon the floor 11, along which they are moved by a paddle 51,

which propels them toward an ash outlet 58 through thefloor. The ashesdischarged through outlet 53 enter a, chamber 59, through which shaft 55 extends, and the shaft is provided with screw flights 60, which advance the ashes through the chamber to the bottom of an upwardly inclined discharge chamber 6|. A driven shaft. provided with screw fiightsBZ within chamb r 6| ev te the s s thr ugh. e a ber, so that they can be discharged in suitable containers.

1 the o on. o he heater illustrated. the n s s. a. w o a mospher c air, u wa dl throughfthe tuyeres and the bed of they burner. Good operating conditions in a unit suitable for domestic use involve a reduced pressure at the burner of 7; to 1 inches. measured. on a wateir manometer. 'Dueto the upward velocity of air and expanding burning gases, the flow is substantially vertical into and through the combustion zone 36 with negligible by-passing of gas to the fan through the shorter route provided by the open bottom of annular gas space 31.

The expanding hot gases from the firebox deliver heat through wall 21 to the heat convey ing medium, which is circulating upwardly through inner annular leg 29. When the gases reach the top of the combustion zone, they are deflected outwardly and pass through openings 38 into the top of gas space 31, through which they start to travel downwardly. The returned gases, entering the gas space through the tangential opening 50, mix with the hot gases and flow therewith along a spiral path downwardly through the gas space toward the outlet passage 43. The mixture of the returned gases with the hot gases in the manner described causes a gas flow at increased velocity through the gas space 31 and, as a result, good heat exchange is obtained between the gases and the heat conveying medium within the inner and outer legs.

In some instances, it may be desirable to employ a plurality of gas inlet and outlet passages and, in that event, the passages will be relatively narrow and vertically elongated.

In the simpler form of the apparatus, in which only a single annular leg is employed, the hot gases of combustion, as in the apparatus illustrated, rise through the combustion chamber and are deflected outwardly by the bottom of the drum toward the inner surface of the leg. The gases thus deflected mix with those entering the chamber through the gas inlet passage and the gas mixture travels spirally downwardly along the inner surface of the leg to the gas outlet passage.

The increased velocity across the heat exchange surfaces resulting from the spiral movement as compared to a direct downward flow provides substantial improvement in heat transfer. Also the method of recirculation described causes the hot gases to pass over the same surface several times before being eliminated from the system and for this reason also gives an improved heat efficiency. The apparatus thus provides increased heat transfer while at the same time reducing the area of heat exchange surface to a minimum. A further advantage of the new mechanism resides in the control of the recirculated gases provided by the damper which also serves to control the induced draft applied to the burner, thus assuring the introduction of an air stream adequate to produce complete combustion.

A further outstanding advantage of the new apparatus resides in the elimination of difficulties due to fly ash. In normal operation of mechanically fed coal stokers, fine ash particles blown from the burner deposit and build up on the boiler surfaces and in the flue causing a substantial reduction in heat transfer. During extended operation of my apparatus, I have found that the surfaces in contact with the spirally flowing gases remain clear of any deleterious deposit. In changing the direction of flow of the exit gases from the fan by a baffle, the major portion of the ash is thrown out of the gas stream and returns to the system where it drops through advantage, namely, that, at all points, where leakage might normally occur, the air flow will be into the system and the escape of dust or products of combustion into the building will thus be prevented. The ash removal exit is in effect sealed by the presence at all times of a solid body of ashes either in the conveying mechanism or in the discharge chamber leading therefrom. Such an ash seal insures that substantially all of the air entering the system will be through the burner and a delicate control of combustion by thedamper 49 is thus provided. The conduit handling the fan discharge is in open communication with the flue and constant fan operation at full capacity is, therefore, permissible without producing any pressure in this portion of the apparatus.

The increased velocity of gaseous flow in the heat exchange system permits the use of relatively less heat exchange area than in other types of boiler construction. In one typical installation having a heat exchange surface of 38 sq. ft., 250,000 B. t. u. was transferred to the heating fluid with a flue temperature of approximately 500 F. and a fan temperature approximating 600 F.

In the various applications of the apparatus of the invention, any heat conveying medium suitable to accomplish the desired result may be cir- I culated through my novel heat exchange system, either by natural circulation resulting from temperature differentials, or by forced circulation. Thus, in a hot air heating system, the circulating air connections are made to the furnace in a recognized way to produce an efiicient circulation of heating air through the heat exchange system and a fan may be employed to increase circulation through the outside heating circuit. In hot water systems used for heat radiation or for a hot water supply, the inlet and outlet connections are arranged to produce a good liquid flow through the heat exchanger. In a boiler for producing steam, the outlet will normally be situated in the upper part of the drum, and the water feed or condensate return in the lower part of the system.

I claim:

1. In a heater, a heat exchanger which comprises a drum forming a reservoir for the heat conveying medium, spaced inner and outer walls extending downwardly from the drum and forming a hollow leg of generally cylindrical form in communication with the interior of the drum, the leg and drum defining a chamber open at the bottom for admission of hot gases, which rise through the chamber to be deflected outwardly at the bottom of the drum toward the inner surface of the leg, the le having a gas outlet passage extending therethrough near the lower end thereof and a gas inlet passage extending therethrough near the upper end thereof, the inlet passage bein substantially tangential to the inner surface of the leg, the leg being continuous except for said inlet and outlet passages, and means for withdrawing gases from said chamber through the outlet passage and returnin a portion of the withdrawn gases through the inlet passage to mix with the deflected gases and flow therewith spirally downwardly along the inner surface of the leg to the outlet passage.

2. In a heater, a heat exchanger which comprises a drum formin a reservoir for the heat conveying medium, spaced inner and outer walls extending downwardly from the drum and having a hollow leg of generally cylindrical form in @ommunicati n with the interior of the :drum, the ies anddrumaie'fining a chamheriopenat thebottom tor admission of hot gases, which rise through the chamber to The deflecte'd outwardly day the bottom of the :drum toward the inner surrface of the Tlegthe le rliavin'g agasvoutlet' :pasisa ge'extendin therethroughnear theilower end thereof and .a gas in'let passage extendingtherethrough -t1earithe upper end rthel eofi, theinl'et :and (outlet passages being substantially tangential to .thelirin'er sunt'ace of thezlegzand: extendingin directiens at fan angle 'ito one another, the legwba ili'l'g continuous except ior said inlet and outlet passages, and means for withdrawing :gases from said chamber through the ioutlet passage and re turning apertien ofthewwithdravm gases through the inlet passage to mix with the defl'e'cted gases and frow therewith spirally downwardly along'the inn-er surface of the leg to'theoutlet passage.

3.111 a heater, an induced-draft heat exchanger which comprises a drum having are'servoir for heat conveying medium, a downwardlyexterrding outer double-walled leg, the space he- 'tween'ithe walls of the leg being in upper coinmun'ication with the drum, an inner doublewalled leg within and spaced from the outer leg to term therebetween an annular gas space, "the space between the'walls of the inner leg being in communication at 'lts'top with the drum and the spaces between the walls of the two legs being connected :near the lower ends of said legs, the inner leg and drum defining a chamber-open at the bottom to permit the upward entrance of hot gases centrally thereof, the :inner leg having a plurality of gas passages therethrough between the upper :parts of the chamber-and the annular gas spacathe outer leg having an outlet passage extending therethrough near the lower endthere- \of for the passage of gases from the annular space and an inlet passage extending therethrough near the-upper end thereof .for the passage .of-gases into the annular space, the outerleg being continuous except .for said inlet and outlet passages, and means for withdrawing lhot gases from the'annular gas space through said outlet passage and for returning a portion of said gases to the annular space through said inlet passage, said inlet passage extending substantially tan- .gential to the inner surface-of the outer annular leg and said return gases producing a spiral downward gas flow through the annulargas space and inducing an upward gas flow through the chamber.

4. In a heater, aninduced-draft-heat exchanger which comprises a drum forming a. reservoir for heatconveying medium a downwardly-extending outer double-walled leg, the space between the walls of the leg being in upper communication with-the drum, an inner double-walled leg Within and-spaced from the outer leg to form therebetween an annular gas space, the space between the walls of the inner leg being in communication at its top with the drum and the spaces between the walls-of the twolegs being connected near the lower ends of said legs, theinner leg and drum defining a gas combustion chamber open at the bottom to permit the upwardentrance oi hot gases centrallythereof, the inner l'eghaving 'a plurality of gaspassages therethrough between the upper parts of the gas combustionchamber and the annular gas space, the outer leg having a gas outlet passage extending therethrough near "the lower end thereof and a gas inlet passage extendin therethrough :near the upper end thereof, the outer leg being continuous except 'for said inlet and outlet passages, a fan -f.or producing an induced draft within the combustion chamber, means tor conducting hot gases from the lower portion of the annular gasspace and delivering them to the inlet of the fan, randirecirculating means .for returning a "controlled {portion efv the hot gases from the outlet of the .fan to the upper part -of the annular igas space, through said "gas inlet, said gas inlet extending substantially tangential to the inner surface of :the outer annular leg whereby the .hot gasesL-meturned to the upper portion of the annular gas space through the gas inlet spiral downwardly through the annular :gas space.

5. :An induced draft boiler asset iorthimclaim 4 in which thegas outlet passage extends inse direction substantially tangential to the inner surface of the outer annular leg and 1111 a direction:at:an angle to the-gas inletpassage.

"6. induced-draft boiler for heating "water :and producing steam zwhich comprisesia relatively shallow circular drum forming -a water reservoir, anlouterdouble-walled .leg extending downwardly from the outer peripheral portion :of :the drum, the space :between the walls of the :leg being in upper communication with thespace withinthe drum, an inn-er double-walled leg within and spaced from the outer leg to form :therebetween an annular gasspaoe, the space betweemthe walls of the inner :leg being in communication at its top with the space within the drum and the spaces between the walls of the two legs being connected near the lower ends of the :legs, the inner leg and drum defining a :gas combustion 'chamberopenat thebottomto permit the upward "entranceof hot gases centrally thereof, the inner leg having a plurality of gas passages therethrough between the upper parts of the gascombustion chamber and the annular igas space, the outer leg having a gas outlet passage extending therethrougd-near the lower end thereof 'and a gas inlet-passage extending therethroughinearcthe upper end thereof, the outer leg lbeingzcontinuous except for said :inlet and outlet ppassages, -a ,ian

i for producing an induced :draft in the gas comhustion chambena passageway forrhotgasesifrom the gas outlet to the :inlet .of the fan, a :duct leadingrfrom-theiamoutlet, means. for conducting a portion of the gases passing through said :duct to gas inlet so that :a ;portion,of the gases passing through the duct may bereturnedto the annular gas space, the gas inlet extending substantially tangential to the inner :surface of the outer :annular leg so that return ejgases passing therethroughto the upper :portion of the'annular gas space will produce a spiral downwardlflow of gases through the annular space, :and adjustable :da'inpzer means E'f0r regulating the proportions-mi gases ipassing through the duct which are re turned to the :annular space through the of generally cylindrical :form :in communication with the interior of the drum, ithef'leg :and drum defining :a :combustion chamber :open vat the :hOttom fortheadmisslonof hotigasesoftc'ombustion fromzthe firebox, which rise throuighithephamber to be deflected outwardly by the bottom of the drum toward the inner surface of the leg, the leg having a gas outlet passage extending therethrough near the lower end thereof and a gas inlet passage extending therethrough near the upper end thereof, the inlet passage being substantially tangential to the inner surface of the leg, the leg being continuous except for said inner and outer passages, and means for withdrawing gases from the combustion chamber through the outlet passage and returning a portion of the withdrawn gases through the inlet passage to mix with the deflected gases and flow therewith spirally downwardly along the inner surface of the leg to the outlet passage.

8. An induced-draft heater which comprises a firebox, means within the firebox for burning fuel, an inlet for introducing combustion air into the firebox, a boiler including a drum forming a water reservoir, 2. downwardly-extending outer doublewalled leg, the space between the walls of the leg being in upper communication with the space within the drum and an inner double-walled le within and spaced from the outer leg to form therebetween an annular gas space, the space between the walls of the inner leg being in communication at its top with the space within the drum and the spaces between the walls of the two legs being connected near the lower ends of the legs, the inner leg and drum defining a vertical combustion zone open at its lower end to the firebox to permit the upward entrance of hot gases from the firebox centrally thereof, the inner leg having a plurality of gas passages therethrough between the upper parts of the combustion chamber and the annular gas space, the outer leg having a gas outlet passage extending therethrough near the lower end thereof and a gas inlet passage extending therethrough near the upper end thereof, the inlet passage being substantially tangential to the inner surface of the outer leg, the outer leg being substantially continuous except for said inlet and outlet passages, means for withdrawing by induced draft hot gases from the combustion chamber through the outlet passage, and recirculating means for returning a controlled portion of the Withdrawn hot gases to the upper part of the annular gas space, through the gas inlet, to mix with the deflected gases and flow therewith spirally downwardly through the annular gas space.

JOHN FARLEY FISHER.

REFERENQES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 326,907 Stilwell July 24, 1906 1,284,053 Briggs Nov. 5, 1918 1,749,907 Dyar Mar. 11, 1930 2,173,115 Hutto Sept. 19, 1939 FOREIGN PATENTS Number Country Date 3,811 Great Britain Mar. 3, 1891 

